1. Field of the invention
The invention relates to the use of combinations of specific polymeric thickening agents and surfactants as thickener systems for high water based functional fluids.
2. Background information
In the context of the present invention, functional fluids are taken to mean hydraulic fluids, metal-working fluids (cooling lubricants) and metal-hardening media. Those functional fluids whose water content is either more than 90% by weight, if no low molecular weight glycols are used concomitantly, or more than 70% by weight, preferably more than 80% by weight, in the case where relatively large proportions of low molecular weight glycols, such as ethylene glycol, diethylene glycol, propylene glycol or dipropylene glycol, are employed besides the water as diluents are designated "high water based" in the context of the present invention.
Efforts have been made for about 25 years to replace the flammable mineral oils and mineral oil products which have been hitherto used as functional fluids by inflammable aqueous fluids. This development has, in the meantime, led to aqueous functional fluids with water contents above 90% by weight (so-called "viscous high water-based fluids"). As thickening agents for the preparation of these high water based functional fluids, water-soluble polymeric polyether(poly)ols or combinations of these polymeric polyether(poly)ols with further auxiliaries have been proposed in particular. Thus, polymeric water-soluble polyether polyols incorporating urethane groups are described for the abovementioned purpose in U.S. Pat. No. 4,481,367, in EP-A No. 1-0 031 777 and JA-A No. 1-41 300/81, and polyether monoalcohols modified with long-chain 1,2-epoxyalkanes are described for the above-mentioned purpose in German Patent Specification No. 3,302,465 and U.S. Pat No. 4,288,639. Combinations of these modified polyether monoalcohols with acidic phosphoric acid esters of non-ionic polyether monoalcohol emulsifiers are known from U.S. Pat. Nos. 4,310,436 and 4,395,351 and combinations of these modified polyether monoalcohols with specific polyether esters, acidic phosphoric acid esters of non-ionic polyether monoalcohol emulsifiers and specific sulphurized metal compounds are described in Canadian Patent Specification No. 1,163,041.
Polymeric water-soluble polyether polyols which are modified with long-chain 1,2-epoxyalkanes and their use as thickening agents for high water based functional fluids are described in EP-A No. 1-61 822, WO-A1-84/00361 and in U.S. Pat. Nos. 4,354,956 and 4,411,819. Combinations of these modified water-soluble polymeric polyether polyols with further auxiliaries are known from numerous patent specifications. Thus, for example, combinations of these modified polyether polyols with acidic phosphoric acid esters of non-ionic polyether monoalcohol emulsifiers are described in EP-B No. 1-63 854, with ethoxylated sorbitol monostearates in EP-B No. 1-61 823, with neocarboxylic acids in U.S. Pat. No. 4,390,439 or longer-chain fatty acids in U.S. Pat. No. 4,390,440, with non-ionic surfactants of certain structural classes in EP-A No. 2-122 528, with specific amines and acidic phosphoric acid esters of non-ionic polyether monoalcohol emulsifiers in U.S. Pat No. 4,312,775, with specific polyether esters, defined sulphurized metal compounds and corrosion-inhibitors in U.S. Pat. No 4,312,768 and with lubricity modifiers, dispersing agents and certain high-pressure additives in U.S. Pat. No. 4,481,125.
These known polymeric water-soluble polyether polyols, employed as thickening agents or thickener systems for high water based functional fluids, and combinations thereof with further auxiliaries have, however, the disadvantage that the functional fluids which have been thickened with them are not resistant to shearing, but instead their viscosity is changed under the influence of shearing forces (for example pressure). Resistance to shearing is, however, one of the most important properties of functional fluids. For hydraulic fluids in particular, a viscosity which is independent of shearing forces is absolutely necessary.